Ceramic Processing Goes Micro

Processing Ceramic Substrates
September 29, 2015
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Ceramic Processing Goes Micro

Ceramic processing goes micro

Microprocessing of ceramic substrates using fiber lasers
Traditionally, ceramics have been processed with CO2 laser technology, but just over three years ago, Synchron Laser successfully utilized the high brightness of near infrared fiber lasers in a proprietary process –today, the results speak for themselves.

Brett Moon, Richard Budd, Andy Appleyard

Scribing and micromachining of AlN and Al2O3 ceramics has been dominated by the use of CO2 lasers for 30 years, the simple reason being that the 10.6µm wavelength has been the one best suited to processing these types of materials. Nevertheless, feature size and finish quality of the ceramic substrates used for electronics applications had changed little in the last 20 years.

However, times are now rapidly changing, with LED and automotive sectors demanding miniaturization, higher accuracy and greater flexibility in the ceramic sub-componentry integrated into their assemblies, all at no expense in terms of throughput and production efficiency.

Synchron Laser of Plymouth, Michigan, USA started using fiber lasers in a process that exhibits both improved consistency during processing with finer detail and better finish on the completed substrate. The adoption of fiber lasers into this process also addresses the need to reduce manufacturing costs, offers exceptional reliability and provides for greater flexibility in the process.

Scribing ceramics with lasers

In general, the use of laser technology benefits the fast pace of development in the electronics industry, providing for flexible and cost effective processes that can cater to the rapidly changing demand for new technology for consumer and industrial electronics. These processes are also non-contact and therefore produce less wastage than physical processing techniques.

Figure 1: A typical low density electronics substrate showing vias, alignment cuts and holes as well as the scribes used to separate the individual pieces.

Figure 1: A typical low density electronics substrate showing vias, alignment cuts and holes as well as the scribes used to separate the individual pieces.

Laser technology has been widely used for processing alumina (Al2O3) and aluminium nitride (AlN) ceramic substrates for the electronics industry for 30 years. For separation of the ceramic substrates into individual components, the laser is used to scribe (drill) a series of partial (i.e. blind), high tolerance holes (Figure 1). Due to the optical absorption properties of the most common ceramics, the laser of choice has previously been the CO2 laser. In this process, the optical pulse energy is absorbed over a short interaction length at the surface of the ceramic, resulting in local heating, melting and vaporisation. The holes thus generated penetrate roughly one third of the way through the substrate and will generate a preferential fault line on subsequent fracture. Using an appropriate adaption of this process, vias, slots, locating features and delicate patterns can also be machined into the substrate.

CO2 laser technology is however not without it’s drawbacks. The accompanying heat affected zone (HAZ), in this case caused by partial melting under the peripherie of the focussed spot, is a principal cause of the relatively low resolution and repeatability achievable. The 10.6µm wavelength and the relatively long pulse duration are both contributory to this issue, while CO2 reliability, footprint and maintenance issues, trailing somewhat behind the advances made in other laser technologies, tend to identify this laser platform as technologically out of date, certainly for most microprocessing applications.

A new technique for scribing

Synchron got involved in the laser materials processing industry around 1980. Starting as a laser service organisation with customers around the world, Synchron soon expanded into building turnkey CO2 systems and providing laser jobshop services. Synchron is now an established supplier of OEM CO2 lasers and integrated turnkey systems for heat treating and materials processing applications – primarily for micromachining ceramics – with markets in the USA, Canada and parts of Central and Eastern Europe, as well as Taiwan, Korea and Japan in the Far East.

Synchron realized the limitations of CO2 laser technology in the face of increasingly severe demands from the electronics industry with regards to tolerances and feature size. Initial tests with Nd:YAG lasers for this application only proved that the absorption at 1µm is simply too weak. More specifically, because of the inefficient coupling along with poor beam quality and spot consistency at high powers, not enough energy is deposited in the surface layer with the requisite definition to generate the desired effect. The development of high power fiber lasers with their inherently stable and high quality beam changed all that.

Synchron also went on to develop a surface treatment to enhance the absorption of laser light at these shorter wavelengths on ceramics. The treatment permeates slightly into the surface of the ceramic and enhances the deposition of energy for near infrared laser pulses over a sufficiently short distance to produce the necessary melting and vaporization. To optimize their process, Synchron uses high brightness fiber lasers from SPI Lasers, UK. SPI has been developing fiber lasers for the industrial market for several years, primarily for materials processing applications such as microwelding and microcutting, but also for marking applications.

Figure 2: Comparison of the scribe pits generated by CO2 and fiber lasers, highlighting the HAZ and geometry differential between the two processes.

Figure 2: Comparison of the scribe pits generated by CO2 and fiber lasers, highlighting the HAZ and geometry differential between the two processes.

Synchron’s surface treatment essentially enhances the coupling of the fiber laser beam into the top surface of the ceramic to start the drilling process. The enhanced dynamics of the interaction between the laser pulse and the material surface, coupled together with a custom, high resolution beam delivery system, mean that significantly smaller features can now be realized in ceramic substrates (Figure 2).

Three years on

After more than three years of total development, the results speak for themselves. For the case of what may be now be considered low-end positional and tolerance geometries, the fiber laser systems easily match the throughput of current state-of-the-art CO2.

However, of greater interest is the higher accuracy and finer spot size produced by Synchron’s fiber laser process that provides for geometry capabilities that are simply not possible with CO2 lasers. This development allows circuit designers to dramatically increase circuit densities while holding the same or better production speeds.

Such is the performance of the laser-material interaction that accuracy and repeatability of the process is now strictly limited by the motion system used. High performance linear motor stages hold positional tolerances in the Synchron systems to 1µm or less and dynamic geometry tolerances to around 3µm or less for very small radii of less than 50µm and 1 to 2µm for larger features (Figures 3 & 4).

Figure 3: Kerf edge on a form cut from a ceramic wafer.

Figure 3: Kerf edge on a form cut from a ceramic wafer.

Figure 4: The top side of a typical 75µm diameter via. HAZ extends 11µm out from the edge of hole and they are round to within 2.5µm. It should be noted that these vias are machined (trepanned) features, not single shots.

Figure 4: The top side of a typical 75µm diameter via. HAZ extends 11µm out from the edge of hole and they are round to within 2.5µm. It should be noted that these vias are machined (trepanned) features, not single shots.

Process enhancement through fiber lasers

As already indicated above, fiber lasers provide a unique series of performance features that benefit not only the application discussed here, but a wide spectrum of other materials processing applications too.

Exceptionally high quality beam profile is available at all output powers right across the range of possible pulse parameters, thereby permitting large working distances (stand-off). The high beam quality, coupled together with a high-end optical system translate into high irradiance (brightness) at the focus, enabling high precision processing with minimal HAZ and driving processes traditionally thought unsuitable for near IR laser technology.

For these and other reasons, fiber lasers bring significant advantages for a host of industrial applications. Fiber lasers have been shown to minimize operational costs through a combination of reduced maintenance costs, no alignment or calibration requirements, longer up-times and improved production quality at higher throughputs. Footprint and robustness are further aspects that make the technology suitable for the most challenging of industrial environments.

Advantages for ceramics market

Synchron’s proprietary technique breaks new ground in an industry that, while being a vital part of the production of consumer electronic products, has not matched the technological advances made in other materials processing industries. However, the bar is quickly being raised in this industry – current manufacturing tolerances in the sector are approximately 10µm, but increasingly severe tolerance demands are being placed, in particular, by manufacturers of high brightness LED units and arrays.

Acording to Richard Budd, Senior Engineer at Synchron, “the stunning reduction in feature size that the combination of the fiber laser and our proprietary surface modification process provides finally opens the door for much finer details to be machined into electronics-grade ceramics at volumes – often exceeding 10 million pieces per month – that easily meet the production demands for mass-consumer electronics such as cell phones, music players and for high intensity LEDs for backlighting and automotive applications”.

Synchron now supplies to dual and quad-beam fiber laser processing systems for ceramics, with the bulk of the systems going to destinations in the Pacific Rim. Current systems are installed in a mass production environment for customers that supply circuitry for very high volume consumer electronics, with processing running 24/7 for over 18 months to-date and operating at speeds that are compatible with the production of several million units per month per-system.

Synchron’s surface treatment can be sprayed, dipped or even rolled, and does not require any significant drying time. The application of a surface treatment to the ceramic does not necessarily add an additional step to the process, as some sort of coating step (usually an anti-spattering layer) is common to the established CO2-driven process.

Summary:

CO2 lasers previously dominated mass production of ceramic substrates for the electronics industry, but Synchron’s new process delivers feature accuracy at throughput speeds that are simply unattainable with the incumbant technology. Synchron’s patent pending process thus looks set to shake up a market which has seen little real development in the finished component for more than 20 years – in this respect, we might be witnessing history in the making.

Figure 5: Flat cut into corner of substrate – the curves are to eliminate potential chipping at sharp corners when substrates are automatically loaded

Figure 5: Flat cut into corner of substrate – the curves are to eliminate potential chipping at sharp corners when substrates are automatically loaded

Authors

Brett Moon’s background includes almost two decades of practical laser experience at Synchron Laser. He also holds a Bachelor’s Degree in German and a Master’s Degree in International Business. In 2000 Brett succeeded his father as President of Synchron Laser, Inc. in Plymouth, MI, USA.

Richard Budd has a lifelong background in electronics design and the physical sciences and is Senior Engineer at Synchron Laser in Plymouth, MI, USA. After a stint in the USAF as a microwave communications equipment technician he started at Photon Sources in 1978 as a field engineer before founding Synchron Laser Service in 1980 along with Brett Moon’s father.

Andy Appleyard is Product Line Manager for cw/modulated fiber lasers at SPI Lasers in Southampton, UK.

Contact
Synchron Laser, Inc.
Plymouth, Michigan, USA
Tel.: +1 248 486 0402
Fax: +1 xxx xxx xxxx
www.synchronlaser.com

SPI Lasers UK Ltd.,
Southampton, UK
Tel. +44 (0)1489 779694
Fax: +44 (0)xxxx xxxxxx
www.spilasers.com